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了解农田表层土壤水分的时空变化对反演涝渍害有着十分重要的意义,针对ASAR GM数据特点提出了在没有地面观测数据地区农田大尺度土壤水分的反演方法,即运用MODIS NDVI数据(空间分辨率为250m)的农田作物时序特征提取土地利用现状,并以此来校正ASAR GM数据(空间分辨率为1km)中的混合像素;利用大面积降水后土壤表层湿度水平差异不大的特点,运用非线性回归模型,获取水云模型中的经验系数,运用水云模型将植被和土壤对后向散射的贡献区分开;在获得一个地方长时间土壤后向散射系数空间分布集后,假设其土壤粗糙度不变的情况下,其后向散射系数与土壤表层湿度成正比,运用其时序特征计算出其土壤表层相对体积含水量。运用上述方法,利用79景ASAR GM数据和同时期的MODIS数据,反演了湖北省四湖地区棉田的土壤表层相对体积含水量的时空分布,将其计算值与观测值比较分析后发现,其变化趋势相同、相关系数(R2=0.779,n=25)也很高,圴方根误差为9.63%,表明上述反演方法还是可行了,适用于大尺度农田土壤墒情的反演。
Understanding the temporal and spatial variations of surface soil moisture in farmland is of great significance to the retrieval of waterlogging and waterlogging damage. Based on the characteristics of ASAR GM data, a large-scale inversion of soil moisture in farmland without ground-based observational data is proposed, using MODIS NDVI data With a resolution of 250m), the current situation of crop utilization was extracted and the mixed pixels in ASAR GM data (spatial resolution of 1km) were corrected. Based on the fact that there was no significant difference in surface soil moisture after large area precipitation, Using the non-linear regression model, the empirical coefficient in the water cloud model is obtained, and the contribution of vegetation and soil to backscattering is distinguished by using the water cloud model. After obtaining the spatial distribution set of the soil backscattering coefficient for a long time, When the soil roughness is constant, the backscattering coefficient is proportional to the surface soil moisture, and the relative volumetric water content of the soil surface is calculated using its temporal characteristics. Using the above method, using ASAR GM data and MODIS data from the same period, the spatio-temporal distribution of relative surface water content of cotton soil in the four lakes of Hubei Province was inversed. Comparing the calculated and observed values, The correlation coefficient (R2 = 0.779, n = 25) was also high, and the root mean square error was 9.63%, which indicated that the above inversion method was feasible and suitable for the inversion of soil moisture in large-scale farmland.